We propose to investigate the use of deoxycoformycin, a potent inhibitor of adenosine deaminase (ADA) in the treatment of human T-cell leukemia. In vitro effects of deoxycoformycin and other potentiating drugs on leukemic cells will be determined by measurement of DNA and protein synthesis in leukemic cells. The key enzymes involved in the metabolism of adenosine and deoxyadenosine will be analyzed in order to compare among different subtypes of acute lymphoblastic leukemia and to correlate the enzyme profiles with sensitivity to deoxycoformycin and other drugs. Based on these in vitro studies, clinical trials of deoxycoformycin and other potentiating agents will be conducted in patients whose leukemic cells display in vitro sensitivity. Optimal route, dosage and frequency of administering deoxycoformycin will be determined from pharmacokinetic studies of deoxycoformycin. The therapeutic responses to deoxycoformycin will be evaluated by observing clinical course, assessing leukemic cell burden and determining the viability of leukemic cells. The possible toxic side-effects of deoxycoformycin will be assessed by clinical observations and routine laboratory tests of functions of major organ systems with special emphasis on hemotological and immunological systems. In addition, the purine metabolism in leukemia cells undergoing treatment with deoxycoformycin will be investigated by high pressure liquid chromatography to elucidate the molecular action of deoxycoformycin, and to obtain quantitative chemical measures by which to assess optimal dose schedules.